Various types of overcurrent protection circuitry are known for AC power transistor switching circuits. The higher the level of sensitivity desired, the higher the degree of sophistication required. A tradeoff is the switching speed, which decreases as the number of intermediate components increases. The present invention overcomes this tradeoff and affords both of the previously incompatable results of simplicity and fast speed in the protective circuitry.
The present invention uses the AC switching device itself for current level detection, affording both accuracy and quick direct detection. The invention eliminates auxiliary sensing devices such as shunts, current transformers and the like. Instead, the invention uses a portion of the switch already in the main AC current path for each direction current flow.